ref: d39d1a5303541539f61488317b220c1eb724d7d3
dir: /sys/src/cmd/jpg/writegif.c/
#include <u.h>
#include <libc.h>
#include <draw.h>
#include <memdraw.h>
#include <bio.h>
#include "imagefile.h"
enum
{
Nhash = 4001,
Nbuf = 300,
};
typedef struct Entry Entry;
typedef struct IO IO;
struct Entry
{
int index;
int prefix;
int exten;
Entry *next;
};
struct IO
{
Biobuf *fd;
uchar buf[Nbuf];
int i;
int nbits; /* bits in right side of shift register */
int sreg; /* shift register */
};
static Rectangle mainrect;
static Entry tbl[4096];
static uchar *colormap[5]; /* one for each ldepth: GREY1 GREY2 GREY4 CMAP8=rgbv plus GREY8 */
#define GREYMAP 4
static int colormapsize[] = { 2, 4, 16, 256, 256 }; /* 2 for zero is an odd property of GIF */
static void writeheader(Biobuf*, Rectangle, int, ulong, int);
static void writedescriptor(Biobuf*, Rectangle);
static char* writedata(Biobuf*, Image*, Memimage*);
static void writetrailer(Biobuf *fd);
static void writecomment(Biobuf *fd, char*);
static void writegraphiccontrol(Biobuf *fd, int, int);
static void* gifmalloc(ulong);
static void encode(Biobuf*, Rectangle, int, uchar*, uint);
static
char*
startgif0(Biobuf *fd, ulong chan, Rectangle r, int depth, int loopcount)
{
int i;
for(i=0; i<nelem(tbl); i++)
tbl[i] = (Entry){i, -1, i, nil};
switch(chan){
case GREY1:
case GREY2:
case GREY4:
case CMAP8:
case GREY8:
break;
default:
return "WriteGIF: can't handle channel type";
}
mainrect = r;
writeheader(fd, r, depth, chan, loopcount);
return nil;
}
char*
startgif(Biobuf *fd, Image *image, int loopcount)
{
return startgif0(fd, image->chan, image->r, image->depth, loopcount);
}
char*
memstartgif(Biobuf *fd, Memimage *memimage, int loopcount)
{
return startgif0(fd, memimage->chan, memimage->r, memimage->depth, loopcount);
}
static
char*
writegif0(Biobuf *fd, Image *image, Memimage *memimage, ulong chan, Rectangle r, char *comment, int dt, int trans)
{
char *err;
switch(chan){
case GREY1:
case GREY2:
case GREY4:
case CMAP8:
case GREY8:
break;
default:
return "WriteGIF: can't handle channel type";
}
writecomment(fd, comment);
writegraphiccontrol(fd, dt, trans);
writedescriptor(fd, r);
err = writedata(fd, image, memimage);
if(err != nil)
return err;
return nil;
}
char*
writegif(Biobuf *fd, Image *image, char *comment, int dt, int trans)
{
return writegif0(fd, image, nil, image->chan, image->r, comment, dt, trans);
}
char*
memwritegif(Biobuf *fd, Memimage *memimage, char *comment, int dt, int trans)
{
return writegif0(fd, nil, memimage, memimage->chan, memimage->r, comment, dt, trans);
}
/*
* Write little-endian 16-bit integer
*/
static
void
put2(Biobuf *fd, int i)
{
Bputc(fd, i);
Bputc(fd, i>>8);
}
/*
* Get color map for all ldepths, in format suitable for writing out
*/
static
void
getcolormap(void)
{
int i, col;
ulong rgb;
uchar *c;
if(colormap[0] != nil)
return;
for(i=0; i<nelem(colormap); i++)
colormap[i] = gifmalloc(3* colormapsize[i]);
c = colormap[GREYMAP]; /* GREY8 */
for(i=0; i<256; i++){
c[3*i+0] = i; /* red */
c[3*i+1] = i; /* green */
c[3*i+2] = i; /* blue */
}
c = colormap[3]; /* RGBV */
for(i=0; i<256; i++){
rgb = cmap2rgb(i);
c[3*i+0] = (rgb>>16) & 0xFF; /* red */
c[3*i+1] = (rgb>> 8) & 0xFF; /* green */
c[3*i+2] = (rgb>> 0) & 0xFF; /* blue */
}
c = colormap[2]; /* GREY4 */
for(i=0; i<16; i++){
col = (i<<4)|i;
rgb = cmap2rgb(col);
c[3*i+0] = (rgb>>16) & 0xFF; /* red */
c[3*i+1] = (rgb>> 8) & 0xFF; /* green */
c[3*i+2] = (rgb>> 0) & 0xFF; /* blue */
}
c = colormap[1]; /* GREY2 */
for(i=0; i<4; i++){
col = (i<<6)|(i<<4)|(i<<2)|i;
rgb = cmap2rgb(col);
c[3*i+0] = (rgb>>16) & 0xFF; /* red */
c[3*i+1] = (rgb>> 8) & 0xFF; /* green */
c[3*i+2] = (rgb>> 0) & 0xFF; /* blue */
}
c = colormap[0]; /* GREY1 */
for(i=0; i<2; i++){
if(i == 0)
col = 0;
else
col = 0xFF;
rgb = cmap2rgb(col);
c[3*i+0] = (rgb>>16) & 0xFF; /* red */
c[3*i+1] = (rgb>> 8) & 0xFF; /* green */
c[3*i+2] = (rgb>> 0) & 0xFF; /* blue */
}
}
/* imported from libdraw/arith.c to permit an extern log2 function */
static int log2[] = {
-1, 0, 1, -1, 2, -1, -1, -1, 3, -1, -1, -1, -1, -1, -1, -1, 4,
-1, -1, -1, -1, -1, -1, -1, 4 /* BUG */, -1, -1, -1, -1, -1, -1, -1, 5
};
/*
* Write header, logical screen descriptor, and color map
*/
static
void
writeheader(Biobuf *fd, Rectangle r, int depth, ulong chan, int loopcount)
{
/* Header */
Bprint(fd, "%s", "GIF89a");
/* Logical Screen Descriptor */
put2(fd, Dx(r));
put2(fd, Dy(r));
/* Color table present, 4 bits per color (for RGBV best case), size of color map */
Bputc(fd, (1<<7)|(3<<4)|(depth-1)); /* not right for GREY8, but GIF doesn't let us specify enough bits */
Bputc(fd, 0xFF); /* white background (doesn't matter anyway) */
Bputc(fd, 0); /* pixel aspect ratio - unused */
/* Global Color Table */
getcolormap();
if(chan == GREY8)
depth = GREYMAP;
else
depth = log2[depth];
Bwrite(fd, colormap[depth], 3*colormapsize[depth]);
if(loopcount >= 0){ /* hard-to-discover way to force cycled animation */
/* Application Extension with (1 loopcountlo loopcounthi) as data */
Bputc(fd, 0x21);
Bputc(fd, 0xFF);
Bputc(fd, 11);
Bwrite(fd, "NETSCAPE2.0", 11);
Bputc(fd, 3);
Bputc(fd, 1);
put2(fd, loopcount);
Bputc(fd, 0);
}
}
/*
* Write optional comment block
*/
static
void
writecomment(Biobuf *fd, char *comment)
{
int n;
if(comment==nil || comment[0]=='\0')
return;
/* Comment extension and label */
Bputc(fd, 0x21);
Bputc(fd, 0xFE);
/* Comment data */
n = strlen(comment);
if(n > 255)
n = 255;
Bputc(fd, n);
Bwrite(fd, comment, n);
/* Block terminator */
Bputc(fd, 0x00);
}
/*
* Write optional control block (sets Delay Time)
*/
static
void
writegraphiccontrol(Biobuf *fd, int dt, int trans)
{
if(dt < 0 && trans < 0)
return;
/* Comment extension and label and block size*/
Bputc(fd, 0x21);
Bputc(fd, 0xF9);
Bputc(fd, 0x04);
/* Disposal method and other flags (none) */
if(trans >= 0)
Bputc(fd, 0x01);
else
Bputc(fd, 0x00);
/* Delay time, in centisec (argument is millisec for sanity) */
if(dt < 0)
dt = 0;
else if(dt < 10)
dt = 1;
else
dt = (dt+5)/10;
put2(fd, dt);
/* Transparency index */
if(trans < 0)
trans = 0;
Bputc(fd, trans);
/* Block terminator */
Bputc(fd, 0x00);
}
/*
* Write image descriptor
*/
static
void
writedescriptor(Biobuf *fd, Rectangle r)
{
/* Image Separator */
Bputc(fd, 0x2C);
/* Left, top, width, height */
put2(fd, r.min.x-mainrect.min.x);
put2(fd, r.min.y-mainrect.min.y);
put2(fd, Dx(r));
put2(fd, Dy(r));
/* no special processing */
Bputc(fd, 0);
}
/*
* Write data
*/
static
char*
writedata(Biobuf *fd, Image *image, Memimage *memimage)
{
char *err;
uchar *data;
int ndata, depth;
Rectangle r;
if(memimage != nil){
r = memimage->r;
depth = memimage->depth;
}else{
r = image->r;
depth = image->depth;
}
/* LZW Minimum code size */
if(depth == 1)
Bputc(fd, 2);
else
Bputc(fd, depth);
/*
* Read image data into memory
* potentially one extra byte on each end of each scan line
*/
ndata = Dy(r)*(2+(Dx(r)>>(3-log2[depth])));
data = gifmalloc(ndata);
if(memimage != nil)
ndata = unloadmemimage(memimage, r, data, ndata);
else
ndata = unloadimage(image, r, data, ndata);
if(ndata < 0){
err = gifmalloc(ERRMAX);
snprint(err, ERRMAX, "WriteGIF: %r");
free(data);
return err;
}
/* Encode and emit the data */
encode(fd, r, depth, data, ndata);
free(data);
/* Block Terminator */
Bputc(fd, 0);
return nil;
}
/*
* Write trailer
*/
void
endgif(Biobuf *fd)
{
Bputc(fd, 0x3B);
Bflush(fd);
}
void
memendgif(Biobuf *fd)
{
endgif(fd);
}
/*
* Put n bits of c into output at io.buf[i];
*/
static
void
output(IO *io, int c, int n)
{
if(c < 0){
if(io->nbits != 0)
io->buf[io->i++] = io->sreg;
Bputc(io->fd, io->i);
Bwrite(io->fd, io->buf, io->i);
io->nbits = 0;
return;
}
if(io->nbits+n >= 31){
fprint(2, "panic: WriteGIF sr overflow\n");
exits("WriteGIF panic");
}
io->sreg |= c<<io->nbits;
io->nbits += n;
while(io->nbits >= 8){
io->buf[io->i++] = io->sreg;
io->sreg >>= 8;
io->nbits -= 8;
}
if(io->i >= 255){
Bputc(io->fd, 255);
Bwrite(io->fd, io->buf, 255);
memmove(io->buf, io->buf+255, io->i-255);
io->i -= 255;
}
}
/*
* LZW encoder
*/
static
void
encode(Biobuf *fd, Rectangle r, int depth, uchar *data, uint ndata)
{
int i, c, h, csize, prefix, first, sreg, nbits, bitsperpixel;
int CTM, EOD, codesize, ld0, datai, x, ld, pm;
int nentry, maxentry, early;
Entry *e, *oe;
IO *io;
Entry **hash;
first = 1;
ld = log2[depth];
/* ldepth 0 must generate codesize 2 with values 0 and 1 (see the spec.) */
ld0 = ld;
if(ld0 == 0)
ld0 = 1;
codesize = (1<<ld0);
CTM = 1<<codesize;
EOD = CTM+1;
io = gifmalloc(sizeof(IO));
io->fd = fd;
sreg = 0;
nbits = 0;
bitsperpixel = 1<<ld;
pm = (1<<bitsperpixel)-1;
datai = 0;
x = r.min.x;
hash = gifmalloc(Nhash*sizeof(Entry*));
Init:
memset(hash, 0, Nhash*sizeof(Entry*));
csize = codesize+1;
nentry = EOD+1;
maxentry = (1<<csize);
for(i = 0; i<nentry; i++){
e = &tbl[i];
h = (e->prefix<<24) | (e->exten<<8);
h %= Nhash;
if(h < 0)
h += Nhash;
e->next = hash[h];
hash[h] = e;
}
prefix = -1;
if(first)
output(io, CTM, csize);
first = 0;
/*
* Scan over pixels. Because of partially filled bytes on ends of scan lines,
* which must be ignored in the data stream passed to GIF, this is more
* complex than we'd like.
*/
Next:
for(;;){
if(ld != 3){
/* beginning of scan line is difficult; prime the shift register */
if(x == r.min.x){
if(datai == ndata)
break;
sreg = data[datai++];
nbits = 8-((x&(7>>ld))<<ld);
}
x++;
if(x == r.max.x)
x = r.min.x;
}
if(nbits == 0){
if(datai == ndata)
break;
sreg = data[datai++];
nbits = 8;
}
nbits -= bitsperpixel;
c = sreg>>nbits & pm;
h = prefix<<24 | c<<8;
h %= Nhash;
if(h < 0)
h += Nhash;
oe = nil;
for(e = hash[h]; e!=nil; e=e->next){
if(e->prefix == prefix && e->exten == c){
if(oe != nil){
oe->next = e->next;
e->next = hash[h];
hash[h] = e;
}
prefix = e->index;
goto Next;
}
oe = e;
}
output(io, prefix, csize);
early = 0; /* peculiar tiff feature here for reference */
if(nentry == maxentry-early){
if(csize == 12){
nbits += bitsperpixel; /* unget pixel */
x--;
if(ld != 3 && x == r.min.x)
datai--;
output(io, CTM, csize);
goto Init;
}
csize++;
maxentry = (1<<csize);
}
e = &tbl[nentry];
e->prefix = prefix;
e->exten = c;
e->next = hash[h];
hash[h] = e;
prefix = c;
nentry++;
}
output(io, prefix, csize);
output(io, EOD, csize);
output(io, -1, csize);
free(io);
free(hash);
}
static
void*
gifmalloc(ulong sz)
{
void *v;
v = malloc(sz);
if(v == nil) {
fprint(2, "WriteGIF: out of memory allocating %ld\n", sz);
abort();
exits("mem");
}
memset(v, 0, sz);
return v;
}